Arginine as a Precursor of Pyrimidines in Strain L-929 Fibroblasts Infected with Pleuropneumonia- like Organisms*

line for growth (1, 2). The importance of arginine is empha- sized by the fact that it is rapidly depleted from the medium in many primary and established cell strains (3). The L-929 fibroblasts maintained in this laboratory and shown to harbor a pleuropneumonia-like infection also demonstrate a.n